In view of their compact construction, light weight, and low power-consumption, flat panel display devices are being widely developed. Flat panel displays include liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), and vacuum fluorescent displays (VFDs). Owing to the ease with which they are driven, and to their superior ability to display images, LCDs are becoming increasingly popular.
FIG. 1 is a schematic diagram illustrating a section of a typical LCD panel. As illustrated in FIG. 1, an LCD panel 1 generally comprises a lower substrate 5, an upper substrate 3 and a liquid crystal layer 7 disposed therebetween. The lower substrate 5 (also known as the driving device array substrate) includes a plurality of pixels (not shown), in which each pixel includes a driving device or thin film transistor (TFT). The upper substrate 3, also known as the color filter substrate, includes a color filter layer to provide color. The lower and upper substrates 5 and 3 further include pixel electrodes and common electrodes, respectively. An alignment layer is formed on the lower and upper substrates 5 and 3 to align liquid crystal molecules from the liquid crystal layer 7.
The lower substrate 5 and the upper substrate 3 are bonded to one another by a sealant 6 at peripheral regions thereof. A spacer 8 is interposed between the lower and upper substrates 5 and 3 to maintain a constant cell-gap therebetween. Images are displayed as the driving devices in the lower substrate 5 control light transmittance through the liquid crystal layer 7 via the liquid crystal molecules disposed between the lower and upper substrates 5 and 3.
An LCD panel may be fabricated using a driving device array substrate forming process to form driving devices in the lower substrate 5 and a color filter substrate forming process to form the color filter in the upper substrate 3. A spacer and sealant forming process may be employed to complete the fabrication process.
The driving device array substrate forming process typically includes forming a plurality of gate and data lines arranged on the lower substrate 5 to define pixel regions, forming thin film transistors (TFTs) (i.e., the driving devices) in each pixel region with each TFT being connected to a gate and data line, and forming pixel electrodes for driving the liquid crystal layer 7 when signals are applied through the TFTs. The color filter substrate forming process includes forming a black matrix on the upper substrate 3, forming a color filter on the formed black matrix, and forming a common electrode.
The spacer 8 can be a column spacer or a ball spacer. It is difficult to evenly distribute ball spacers on a substrate and maintain a uniform cell gap without reducing the aperture ratio in an LCD panel. Column spacers may be better suited for maintaining a constant cell gap and for preserving the aperture ratio, since they can be formed at predetermined positions throughout the LCD panel.
However, column spacers have their own share of problems. First, they may be unable to prevent a touch inferiority defect at the surface of the LCD device. For example, when a surface portion of an LCD device is swept away, non-uniform brightness at the swept portion may generate a stain. Secondly, a press inferiority defect may occur when the surface of an LCD device is pressed under constant strength. In this case, the color filter substrate or the TFT substrate may be altered so that a corresponding stain is generated.